Never found one so far
I imagine a murderous eternium two-handed sword of penetration would be a stellar item, dealing tons of damage to everything and being virtually indestructible.
I once tested self-flagellation looking for bugs, and noticed a few quirks.
* Prefixes and suffixes, other than those which affect base damage, didn't have any effect.
* The Z value in the whip's XdY+Z damage doesn't apply when calculating damage.
* I was always brought down to 1 HP first, no matter the whip's damage. Healing even one hit point will result in the same effect if you do it again. Whipping yourself at 1 HP will kill you, obviously.
Oh, and it also has a very small chance of curing sickness - although at the stage where this effect would be fairly desirable, it's not a good idea to reduce your HP even more